As runners, our most valuable possessions are our feet. And while our tootsies may not win any beauty contests (hello, black toenails and blisters galore), their overall health is crucial, as it impacts our entire skeletal structure, explains Dr. Jacqueline Sutera, D.P.M. and spokesperson for the American Podiatric Medical Association. Turns out, there are lots of little things we do everyday that set us back on this front.

Here, Sutera and two other podiatrists share the widely-practiced, surprisingly harmful habits that damage our feet—and what we should do instead.

Cutting out an Ingrown Toenail Yourself

Why It’s Bad: “Almost everyone will suffer from an ingrown toenail during their life, whether it be the result of an injury, poor fitting shoes, or genetics,” explains Dr. Amanda Meszaros, an Ohio-based podiatrist. Many will attempt to resolve the issue with “bathroom surgery,” i.e. an at-home, self-directed procedure, often performed with non-sterile, ineffective instruments. A common result: a splinter that will fester, cause an infection, or trigger a fleshy growth called pyogenic granuloma that results from minor trauma.

What to Do Instead: “Seek professional help early,” advises Meszaros, noting that in-office treatment is easy, simple, and offers quick relief of symptoms.

Running a Race or Distance Run in a New Pair of Shoes

Why It’s Bad: “I see many runners who get close to a race and think ‘Oh crap, I better get a new pair of sneakers!’” says Dr. Lori Weisenfeld, NYC sports podiatrist. But even if you purchase the exact same model, running in fresh sneaks can give you blisters and/or shin splints simply because they haven’t been broken in yet. “I tell patients to never opt for new shoes in a competitive or distance situation,” explains Weisenfeld.

What to Do Instead: Once you find a sneaker brand and model that works well for you, purchase several pairs and alternate usage, advises Weisenfeld. This means you’ll always have a backup come race day.

Committing to One Shoe Size

Why It’s Bad: It’s a common misconception that once you reach adulthood, your shoe size is set in stone. “Many of us buy the same shoe size year after year without regard to structural changes, and attribute new discomfort to simply aging or wear and tear,” says Meszaros. But as we get older, she explains, “our ligaments and tendons become more lax, our arch height decreases, and the shock absorbing fat that pads our feet thins and atrophies, especially in women.”

What’s more, people over 40 will generally gain length over time as well—up to half a shoe size per decade of life.

What to Do Instead: Consider periodic professional measurement, recommends Meszaros. Also, rather than automatically purchasing your go-to number, test out new kicks in-store, and become aware of the variances in size by brand.

What to Do Instead: When it comes to running shoes, Weisenfeld abides by the “rule of thumb,” which dictates a thumb’s width distance between your longest toe and the front of the shoe. If your toes are closer to the edge, try the next size up.

Wearing Flats on a Regular Basis

Why It’s Bad: “Many women turn to flats as an alternative at work or for a commute on foot,” says Meszaros, acknowledging the shoes are lightweight, portable and flexible. “But these convenient shoes have little to offer in the way of shock absorption and cause increased pressure on the ball of the foot and heel even with moderate walking.” That lack of support can translate into heel pain from repetitive stress, tendonitis from lack of stability, metatarsalgia (forefoot pain) and stress fractures.

What to Do Instead: “Although athletic shoes with professional attire are frowned upon from a fashion standpoint, newer options in lightweight sport-style shoes in more desirable colors and patterns may provide increased cushioning and less risk of fatigue related injuries,” recommends Meszaros.

Walking Barefoot on Hardwood Floors

Why It’s Bad: When treading on hardwood, cement, stone, or ceramic tile, “there is really nothing to absorb the shock between you and the ground,” explains Sutera. Over time, this behavior can deteriorate your fat pad, which serves as the foot’s natural cushion. Again, women should be especially cognizant of fat pad atrophy, Sutera explains, as they’re more likely to develop it due to hormone changes.

What to Do Instead: Limit your barefoot time to carpet or cork flooring only, and wear comfortable, supportive footgear when on harder indoor surfaces. Sutera’s at-home go-to: plush slippers with a cushy arch support.

Wearing Worn-Out Shoes

Why It’s Bad: Wearing worn-down footwear that doesn’t offer the proper support can hurt not just your feet, but your entire skeleton, reiterates Sutera. “When a shoe is old and worn out, it tilts the way that you stand and walk, and can force your foot to land in a way that’s unnatural and damaging.” Sutera’s response to patients who are reluctant to retire well-worn, cloyingly comfy footwear: “Fast food tastes good, but it’s not good for you. Your favorite old shoes may be harming your health.”

What to Do Instead: Determine your shoe health with the “tabletop test,” says Sutera. Place your footwear on the table and examine it at eye level. If the heel is noticeably worn down and/or deformed, it’s time for a new pair.